This invention relates a tube length control method and apparatus for a tube bending mechanism and, more particularly, is an improvement to the tube bending structures illustrated in U.S. Pat. Nos. 5,233,853 and 5,379,624.
U.S. Pat. No. 5,233,853 discloses a device for simultaneously stretch straightening a plurality of side-by-side oriented segments of tubing for use in manufacturing heat exchangers and bending that tubing to form hairpin tubes. In the process of manufacturing a plurality of hairpin tubes simultaneously, difficulty was being encountered in keeping the legs of the xe2x80x9cUxe2x80x9d of the hairpin tubes to the same length. U.S. Pat. No. 5,379,624 provides a solution to that particular problem, which problem is caused by varying frictional forces occurring as each tube is being bent so that following a bending of a plurality of tubes, the lengths of the respective legs would be substantially different.
Often users of the machines described in the two above referenced patents will process tubing from several different vendors at the same time. As a result, tubing that is side-by-side oriented on the tube bending mechanism behaves differently because of the continuous variations presented thereat due to tube hardness, tube lubrication, tube wall thickness amongst other things. Thus, it is desirable to provide a monitoring of the length of the legs of the xe2x80x9cUxe2x80x9d of each hairpin manufactured and to provide for an automatic variation in the orientation of components to maintain the ends of the legs of the xe2x80x9cUxe2x80x9d coplanar with each other.
Therefore, it is an object of this invention to provide a method and an apparatus which will effectively monitor the length of the legs of the hairpin tubes and automatically implement an adjustment to maintain within tolerance the length of the legs of each hairpin the tube manufactured and the beneficial aspects explained in the two aforementioned patents.
It is an object of the invention to provide a tube bending method and apparatus, as aforesaid, which will monitor and effect an accurate control of the length of the legs of the U-shaped hairpin tube to a prescribed length.
It is a further object of the invention to provide a hairpin bending method and apparatus, as aforesaid, which will facilitate the bending of a plurality of such hairpin tubes simultaneously, each of the plurality of hairpin tubes having legs of a precisely controlled length.
It is a further object of the invention to provide an improvement to the tube bending method and apparatus described and illustrated in U.S. Pat. Nos. 5,233,853 and 5,379,624.
In general, the objects and purposes of the invention are met by providing a tube bending method for bending and a tube bending mechanism configured to bend a finite length tube section supplied by a finite length tube supply into a U-shape, at least one end of the tube section being pushed by a pusher to a desired location. A tube end locating device is configured to locate at least one of first and second ends of the tube section following a bending operation and produce a signal indicative of a distance of one of the two ends from a bend axis of the U-shaped tube, the signal being indicative of one of the two ends being either too short or too long. A support is provided for supporting either the pusher or said tube bending mechanism at an adjustable distance from the finite length tube supply for facilitating adjustable relocation before a start of a next cycle of operation of the tube bending mechanism. A control mechanism responsive to the signal is provided to effect an adjustable relocation of either the pusher or the tube bending mechanism from the finite length tube supply so that following a next cycle of operation of the tube bending mechanism, at least one of the two ends will be oriented at least closer to the desired location.